Jacobsite: Properties and Occurrences

Jacobsite is a manganese iron oxide mineral. It is in the spinel group and forms a solid solution series with magnetite. The chemical formula is MnFe2O4 or with oxidation states and substitutions: (Mn2+, Fe2+, Mg) (Fe3+, Mn3+)2O4. It is a black magnetic isometric mineral consisting of an oxide of manganese and iron and constituting a member of the magnetite series.

It was first described in 1869 and named for the Jakobsberg Mine, Nordmark, Filipstad, Värmland, Sweden.

General Information

  • Category: Oxide minerals (Spinel structural group
  • Formula: iron(II, III) manganese oxide, MnFe2O4
  • Crystal system: Isometric
  • Crystal class: Hexoctahedral (m3m)

Fig: Jacobsite Рa manganese iron oxide mineral

Properties

Jacobsite forms opaque to translucent, black to brownish black crystals or coarse to fine granular masses with metallic to a submetallic luster. It is a manganese iron oxide mineral, a member of the magnetite, series of spinels.

  • Color: Black to brownish black
  • Crystal habit: Disseminated to massive, rarely as octahedral crystals
  • Fracture: Conchoidal
  • Mohs scale hardness: 5.5 – 6.5
  • Luster: Metallic
  • Streak: reddish black to brown
  • Diaphaneity: Opaque
  • Specific gravity: 4.76
  • Optical properties: Isotropic

Occurrence: A primary mineral or an alteration product of other manganese-bearing minerals in some metamorphosed manganese deposits.

It occurs as a primary phase or an alteration of other manganese minerals during metamorphism of manganese deposits. Typically associated minerals include hausmannite, galaxite, braunite, pyrolusite, coronadite, hematite, and magnetite.

Association: Hausmannite, galaxite, braunite, pyrolusite, coronadite, hematite, magnetite.

 

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